Even mother whales need a minute

Being a mom can be exhausting work. Taking a break every now and then is essential for mothers of many species, including whales. And that could be the motivation behind a particular habit of some southern right whales (Eubalaena australis), the only species of whale known to turn over.

“It’s definitely unusual behavior,” says Renae van Noort, a conservation biologist at the University of Western Australia. “It looks quite strange, especially when you see them from a distance with their pectoral fins out of the water.”

Southern right whale mothers lead extreme lives. They spend months eating and storing energy in Antarctica, then embark on long migrations to reach their calving grounds, where they give birth and care for their young, all without eating for months. At this crucial time, resting and saving energy becomes a matter of life and death, as they need enough food to feed their young and return to their feeding grounds, where they can finally eat again.

On supporting science journalism

If you enjoy this article, please consider supporting our award-winning journalism by subscribe. By purchasing a subscription, you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

Van Noort and his team decided to take a closer look at how these mother whales conserve energy by filming them and their calves using drones in South Australia’s Head of the Bight Bay, where southern right whales congregate and give birth. Some 75 hours of footage of 90 mother-cub pairs showed that the mothers spent an average of 33 percent of their time restingthe team reported on July 6 in Mammal biology. The calves also rested, especially when their mothers were also resting.

Cetaceans most often rested while floating, dorsal side up, on the surface as well as below. But some mothers – 25% of the total – also had another strategy: resting upside down. “We still don’t know why some mothers rest this way and others don’t,” says van Noort.

This behavior only occurs in southern right whales. This could be because mothers in other species have different ways of conserving energy, says Malin Lilley, a comparative psychologist at Texas A&M University who was not involved in the new study. “Or, they might not rest in habitats as undisturbed by human activity as this particular population of southern right whales,” she adds. Rolling on their backs makes whales more vulnerable to collisions with ships.

Mothers rarely rolled onto their backs – only 2% of their time – both below and above the surface of the water. The team documented the behavior only in lactating mothers and in one pregnant whale, suggesting that getting into this position might be nothing more than a way for mother whales to take a break. When lying upside down, their calves can’t reach the mammary slits to get milk, meaning mothers can decide when it’s feeding time.

Lying upside down can also help regulate their temperature, cooling it with the cool air hitting their fins.

Lilley says future research could study how and when mother whales learn to rest in this position. “They might learn from their own mother, from their previous experiences with calves or perhaps from observing other mothers,” she says.